24 HOW TO SEE WITH THE MICROSCOPE. 



Aside from these matters involving sound mechanism, 

 there remain other points connected with the choice of 

 a stand, which may, to some extent, be regarded as a 

 matter of election. For instance, some of the most 

 costly stands are furnished with mechanical stages 

 whereby motions are given to the object-carrier by 

 various milled heads. I have used these stages in times 

 past, anc 1 have to record my disapprobation of them, 

 and for the following reasons: 



FIRST. They are an impediment to quick work. It 

 is much quicker to run from one end of an object to 

 another by one single movement given by hand than 

 to wait the slow motions of the screws. There are, how- 

 ever, some advantages arising at times from the use of 

 the mechanical sta^e, e, g., in adjusting the image of an 

 object to the eye-piece micrometer, etc. Nevertheless 

 these slight conveniences are sadly outweighed by the 

 positive objection to their use. 



SECOND. A mechanical stage, to be good for any 

 thing must be nicely made ; hence they are costly, and 

 further, seldom keep in order for a great length of time, 

 however well made. 



THIRD. As generally modelled, they increase the 

 thickness of the stage, and the screws are always more 

 or less in the way. 



FOURTH. Those who rely on their mechanical assist- 

 ance seldom arrive at that delicate finger manipulation 

 so necessary to be acquired by the observer. Any one 

 of the objections above named ought, in my opinion, to 

 be sufficient and determinate. 



